3. DDS + AMP
Amplifier has abt. 35 dB of gain. In practice, there will be necessary to add external attenuators (20 dB resp. 10 dB) in every channel between DDS output and AMP input to have possibility to change continuously output level beginning from 0 dBm to the possible maximum. Connection is possible thru rear panel connectors.
The following two pictures show that level of the second harmonic in both cases is unacceptable high (20dB attenuator was used at the Spectrum Analyzer input). Next two pictures show oscillograph record of AMP output signals for minimum and maximum signal level incoming from DDS and confirms that amplifiers working outside of linear range of its characteristic. I checked that below +25 dBm the output signal has sinusoidal profile. It will be always necessary to use LPFs along with amplifiers, regardless of signal level. It can be to the benefit of IM features of the entire set.